1. Field of the Invention (Technical Field)
The invention described and claimed herein is generally related to earth moving machines and apparatus. More particularly, the present invention is related to padding machines.
2. Description of the Related Art Including Information Disclosed under 37 C.F.R. .sctn..sctn.1.97-1.99 (Background Art)
Underground cables and pipelines are typically emplaced by laying the cable or pipeline in a prepared trench and subsequently backfilling the trench.
Some cables and pipelines are susceptible to damage from stones or other hard objects in the backfill material. For example, optical fiber communications cables are considered particularly susceptible to damage in this manner, as are polymeric or plastic pipelines. Also, steel pipes are increasingly provided with protective polymeric coatings, which must be protected from penetration or damage by hard objects.
Consequently, in the laying of cables and pipelines it is increasingly sought to backfill the trench with fill material that is relatively free of stones or other hard objects. One way to achieve this is to backfill the trench with sand or other suitable fill material brought from a remote source of sand or rock-free soil. This approach is however relatively expensive and time-consuming. Further, where steel pipe is covered with a layer of sand, the filled trench tends to collect standing water in the porous sand fill, leading to premature corrosion of the pipe. Also, the use of a fill material that is different from the surrounding soil results in a loss of cathodic protection, which also leads to premature corrosion of steel pipe.
The alternative is to screen the soil dug from the trench, to remove stones and other foreign objects, and return the screened soil to the trench. Several machines, known as padding machines, have been disclosed in the prior art for this purpose. For example, U.S. Pat. No. 2,857,691 to Curran discloses a tracked vehicle having a vertically swingable boom that extends laterally over a trench. The boom includes a tube having an enclosed auger. At the far end of the boom from the vehicle is a rotating head which scoops up soil from alongside the trench, screens the soil, and transmits it to the auger, which conveys the screened soil along the tube and into the trench through openings in the tube. The Curran apparatus is particularly designed for use with a vehicle that is driven along the opposite side of a trench from the pile of soil that was removed from the trench and which extends alongside the trench.
U.S. Pat. No. 4,633,602, to Layh, et al., teaches the use of a gathering belt which dumps material onto a separator screen, allowing fines to fall onto a lateral belt. This device does not provide for screening during the initial conveying nor for attachment to vehicles, such as loaders and bulldozers.
U.S. Pat. No. 3,596,384 to Neujahr employs an auger to remove soil from the piled ridge of soil removed from a trench to a second auger, which conveys the soil to a screen and to a set of impellers which throw the screened soil into the trench.
U.S. Pat. No. 4,301,910 to Price also discloses a self-propelled backfilling machine which utilizes a conveyor belt to transport soil from a hopper into a trench.
U.S. Pat. No. 4,664,791, issued May 12, 1987 to McClain et al., also discloses a padding machine particularly designed to receive backfill material in a hopper and to sieve the material and dispense it into a trench.
The padding machines presently available are generally large machines, which are intended and useful primarily for long-distance pipe laying operations in open country, where rights of way are wide and where there is little or no rugged terrain. Such machines have limited usefulness where rights of way are narrow, where trenches do not follow a straight path, or where the terrain is relatively rugged.